body {
  margin: 0;
  padding: 0;
  background-color: #ff0000;
}
img {
  display: block;
  width: 100%;
}
@keyframes show {
  0% {
    background-position: 0 0, 0 0;
  }
  100% {
    background-position: 500px 500px, 1000px 500px;
  }
}
.show {
  position: fixed;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background: url("./a.png"), url("./b.png");
  animation: 10s show linear infinite;
}
